The Influence of Glacial Northern Hemisphere Ice Sheets On Atmospheric Circulation

Abstract. During the last glacial period, Northern Hemisphere (NH) ice sheets significantly influenced atmospheric circulation, yet their broader impacts beyond the North Atlantic remain underexplored. Using the Australian Earth System Model (ACCESS-ESM1.5), we simulate a glacial climate around 49,000 years ago (49 ka) during Marine Isotope Stage 3 (MIS 3, 65–25 ka), a period marked by prominent millennial-scale variability. Our findings demonstrate that the NH ice sheets induced a southward shift of the NH westerlies, increasing rainfall over Eurasia during boreal summer while reducing it in winter. The ice sheets' influence also extended across the tropics and the Southern Hemisphere (SH), driving a southward displacement of the Intertropical Convergence Zone (ITCZ) and the NH Hadley cell during austral summer, intensifying Australian rainfall. Additionally, including the Laurentide and Antarctic ice sheets (LIS and AIS) shifts the SH Hadley cell and the SH westerlies equatorward during JJA. These findings highlight the non-linear interactions between ice sheets, large-scale atmospheric circulation, and precipitation patterns.